1. Field of the Invention
The present invention relates to a light emitting apparatus using a light emitting element emitting fluorescence or phosphorescence by applying an electric field to an element having a film including an organic compound (hereinafter, described as “organic compound layer”) between a pair of electrodes, and to a method of fabricating the light emitting apparatus. Further, a light emitting apparatus in the specification includes an image display device, a light emitting device or a light source (including illuminating device). Further, a light emitting apparatus includes all of a module of a light emitting apparatus attached with a connector, for example, FPC (Flexible Printed Circuit) or TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package), a module provided with a printed wiring board at a front end of TAB tape or TCP and a module in which a light emitting element is directly mounted with IC (Integrated Circuit) by COG (Chip On Glass) system.
2. Description of the Related Art
There is expected application of a light emitting element using an organic compound characterized in thin shape, light weight, high response and direct current voltage drive as a light emitting body to a flat panel display of next generation. Particularly, a display apparatus arranged with light emitting elements in a matrix-like shape seems to be superior to a liquid crystal display apparatus of a related art in view of wide viewing angle and excellence in optical recognizing performance.
According to the light emitting mechanism of a light emitting element, it is said that by interposing an organic compound layer between a pair of electrodes and applying voltage, an electron injected from a cathode and a hole injected from an anode are recombined at a center of light emission in the organic compound layer to form molecular exciton and when the molecular exciton returns to the ground state, energy is discharged to emit light. There are known singlet excitation and triplet excitation in an excited state and it seems that light can be emitted by way of either of the excited states.
It is possible to use driving methods of passive matrix drive (simple matrix type) and active matrix drive (active matrix type) for such a light emitting apparatus formed by arranging light emitting elements in a matrix-like shape. However, when a pixel density is increased, the active matrix type provided with a switch for each pixel (or dot) is advantageous since the active matrix type can be driven at low voltage.
Further, although a low molecular species material and a high molecular species (polymer species) material are respectively researched for an the organic compound for constituting the organic compound layer (strictly speaking, light emitting layer) regarded to be the core of a light emitting element, more attention is given to the high molecular species material facilitated to handle and having high heat resistance than the low molecular species material.
Further, although there are known methods such as vapor deposition method, spin coating method and ink jet method for a film forming method of the organic compounds, as a method for realizing full color formation by using the high molecular species material, spin coating method and ink jet method are particularly well known.
The light emitting elements having the organic compounds has a defect that is easy to be deteriorated by various factors, therefore it is a maximum object of the light emitting elements to be formed with high reliability (long lifetime).
Here, in a light emitting element using an organic compound, we will consider the pathway in which an electron and a hole injected from an electrode are converted to photon and finally brought out to the outside of the element. Among the currents passing through an external circuit, only some fractions thereof contribute to the carrier combination as electron-hole pairs and part of the recombined electron-hole pairs is consumed in the generation of luminescent molecular excitons. The generated excitons are converted to photon as much as being defined by fluorescent quantum efficiency. The remainder thereof is deactivated in various pathways, for example thermal deactivation and the generation of infrared light. Therefore, when such a light emitting element is actuated to allow the light emission, the generation of Joule heat occurs, leading to the decomposition or crystallization of an organic compound to cause the degradation of the light emitting element.